The respective jobs of copying, printing, scanning, and faxing processed by an integrated application are unitarily divided into four job steps. A package of function modules 41A selectively used in the respective jobs is classified into four groups of input, create, edit, and output function modules 410 to 412 according to the division. A data format is unified into bitmap by a create function module 411A, and the bitmap data is processed by an edit function module 411B for pagination or aggregation, etc. In response to receiving setting information and a job code, a job controlling module 43A creates job step control blocks 440 to 442 and writes the information therein to create a job. Each of job step controlling (JSC) modules 450 to 452 starts a function module for each page, and after the completion thereof, creates a thread control block for the next downstream side JSC module.